1864] 



Prof. Guthrie on Drops. 



479 



wards through a third liquid C, is intermediate hetween the drop-size of 

 A through C and that of B through C ; and the greater the proportion of 



■g there is in the mixture, the more nearly does the di^op-size of the mix- 



A. 



ture approach to the drop-size of ^ alone. 



It is remarkable that supplementary drops are found in the cases just 

 considered, just as in the case of water dropping through the same liquids. 

 But the supplementary drops of benzol and turpentol through water bea;- 

 a much smaller ratio to the main drops than do those of water through 

 benzol and turpentol to their main drops. Judging only from the equality 

 in their rate of ascent through the measuring-tube, all these supplementary 

 drops are very exactly of the same size. The supplementary drops were 

 not further examined, but were always collected and measured with the 

 main drops. 



Viewed as a means of quantitative chemical analysis, the measurement 

 of the drop-sizes of liquids which drop up through water is yet more 

 sensitive than that of the drop-sizes of water falling downwards through 

 the liquids. Thus, from Table XVII., the least proportional difference of 

 drop-number, caused by an alteration in the proportion of the liquids, is 

 between T and BT2, where a diminution of 33*33 per cent, in the turpen- 

 tol and an addition of 33*33 per cent, of benzol causes a difference of 35*3 

 in the drop-number. 



Liquid T. BT2. BT. B^T. B. 



, rB= 33*33 50 66'66 100 



Percentage.. 1^^^^^ ^^.^^ ^^.^^ ^ 



Difference offB 33*33 16*66 16*66 33*33 



percentage. . (T 33*33 16*66 16*66 33*33 



Difference of) 3^.3 21*7 24*3 102*0 



drop-number J 



Or this stalagmometer shows the composition of the liquid to within 

 1 per cent. Further, if the mixture contain less than one-third of benzol, 

 we could determine the proportion, on an average, to within 0*33 per cent. 



It may be noticed with regard to SLL that the value of gt is of much 

 less influence upon the drop-size than in the case SLG. It is generally 

 sufficient in the former case that the average value of gt should be con- 

 stant. This is especially the case where the drops are formed from a tube 

 (as the end of a siphon), and not from a convex solid. The reason is 

 obviously that in the former case the thickness of the residual film, upon 

 which we have found the size to depend, is at all rates indefinitely great, 

 while in the latter case it depends upon the rate of supply. 



In order to compare the drop-size of A through B with that of B through 

 A under quite similar conditions, the siphon A of fig. 10 was inverted and 

 applied to the cup stalagmometer of fig. 7. The arrangement of the end 

 is seen in fig. 11. In using this form of stalagmometer, the end of the 

 delivery-siphon must be at first wiped dry, so that the water may not 



